1. Field of the Invention
The present invention relates to a shock absorbing steering apparatus which can absorb the shock from a steering column upon the collision of a vehicle to protect a driver or passenger.
2. Related Background Art
Upon the collision of a motor vehicle, subsequent to a so-called primary collision where the motor vehicle strikes against another motor vehicle, there arises a so-called secondary collision where a driver is struck against a steering wheel of the vehicle. In the secondary collision, in order to protect the driver's life by reducing the impact or shock to which the driver is subjected, it has generally been attempted that a steering shaft having one end to which a steering wheel is secured was made collapsible so that the total length of the steering shaft is reduced upon acting the strong impact on the shaft and a steering column through which the steering shaft extends was made of shock absorbing material.
In the past, a shock absorbing steering apparatus used for this purpose is already known, as disclosed in the Japanese Utility Model Laid-Open Appln. No. 63-76578. The details thereof will be described with reference to FIGS. 21 to 24.
In FIG. 21, a steering shaft 201 has a steering wheel 202 attached to an upper end of the shaft so that the steering shaft can be rotated around its own axis when the steering wheel is turned. The steering shaft 201 has a collapsible arrangement (not shown) wherein the total length of the shaft can be reduced when an axial impact is applied to the shaft.
A steering column 203 has a cylindrical body into which the steering shaft 201 is inserted, and the cylindrical body is supported, at its intermediate and lower portions, by a vehicle body 204 such as an undersurface of a dashboard, via upper and lower support brackets 206, 205, respectively. The steering column 203 has also a so-called collapsible arrangement (not shown) wherein the total length of the column can be reduced while absorbing the shock when an axial impact is applied to the column.
The upper support bracket 206 is formed by bending a metal plate and is secured to the outer surface of the steering column 203, for example, by welding. The bracket 206 is provided at its both lateral ends with attachment plate portions 207 by which the upper support bracket 206 is attached to the vehicle body 204. Each attachment plate portion 207 has a U-shaped open slot 208 at its one edge (near the steering wheel 202).
A locking member 209 has a U-shaped body made of synthetic resin and is attached to one edge portion of each attachment plate 207 to cover the slot 208. By tightening a bolt 210 passing through a through hole 215 formed in the locking member 209 and the slot 208 into a threaded hole (not shown) formed in the vehicle body 204, each attachment plate 207 is firmly pinched by the corresponding locking member 209 and the upper support bracket 206 is supported by the vehicle body 204 via the locking members 209.
Further, an energy absorbing member 211 having an intermediate bent portion 212 is attached, at its one end, to each attachment plate portion 207 by welding. The other end of each energy absorbing member 211 is connected to the corresponding locking member 209 via the above-mentioned bolt 210 which also passes through a through hole 216 formed in the energy absorbing member. Each energy absorbing member 211 is made of a plastically deformable sheet plate and its U-shaped intermediate bent portion 212 is pinched by the corresponding attachment plate portion 207 (from above) and a guide plate 213 (from below) which will be described later.
Each guide plate 213 is formed from the sheet metal by press working. The guide plates 213 are secured to the upper support bracket 206 on both sides thereof below the corresponding attachment plate portions 207, by welding, so that a guide space 214 for guiding the bent portion 212 of the energy absorbing member 211 is formed between each guide plate 213 and the corresponding attachment plate portion 207.
With the arrangement as mentioned above, the shock absorbing steering apparatus will be operated as follows, upon the collision of the vehicle.
In the secondary collision due to the vehicle accident, when the impact is transmitted from the driver to the steering wheel 202, the impact or shock is immediately transmitted to the steering column 203, thus pushing the column 203 in its axial direction strongly. In this case, when the axial impact force applied to the steering column 203 becomes greater than friction forces between attachment plate portions 207 and the locking members 209, the bolts 210 are escaped from the corresponding open slots 208 formed in the attachment plate portions 207, so that the steering column 203 can be freely displaced in the axial direction.
As a result, the steering column 203 is shifted in the axial direction (leftwardly and downwardly in FIG. 21) due to the impact force. Consequently, as shown in FIG. 24, each energy absorbing member 211 tends to be extended. In this way, as each energy absorbing member 211 is being extended, the intermediate bent portion 212 is shifted from one end (right end in FIG. 24) of the member connected to the bolt 210 to the other end (left end) connected to the attachment plate portion 207. During this shifting movement of the bent portion, the various portions of the energy absorbing member 211 are plastically deformed, thus absorbing the shock applied to the steering column 203 from the driver via the steering wheel 202.
The conventional shock absorbing steering apparatus having the above-mentioned construction has the following drawback.
In particular, the apparatus is so designed that, upon the occurrence of the secondary collision, the total length of the collapsible steering column 203 is reduced and at the same time the attachment plate portions 207 of the upper support bracket are slipped out of the corresponding locking members 209. However, the forces required for initiating the reduction in length of the steering column and for initiating the relative slippage between the attachment plate portions 207 and the locking members 209 are considerably greater than the forces required after such reduction and the relative slippage have been started. Accordingly, in the conventional apparatus wherein the reduction in length of the steering column 203 and the relative slippage between the attachment plate portions 207 and the locking members 209 are initiated simultaneously, at a moment when the driver is struck against the steering wheel 203, it is feared that the driver is subjected to the great impact force.
In order to reduce the impact force applied to the driver upon the secondary collision as long as possible, it is desired to reduce the force required for initiating the displacement of the steering wheel 202 upon the secondary collision. For this purpose, for example, the Japanese Patent Laid-Open Appln. No. 61-57462 discloses an arrangement wherein a support bracket itself for supportingly connecting a steering column to a vehicle body can be deformed.
However, in this arrangement, since the support bracket having the great rigidity must be deformed, the force required for initiating the displacement of the steering wheel cannot necessarily be reduced sufficiently. But, if the rigidity of the support bracket is merely reduced, the supporting ability of the bracket will be insufficient; thus, this solution cannot be adopted.